1. Field of the Invention
The present invention relates to the control and stabilization of the flight attitude of an aircraft. More particularly, this invention pertains to an arrangement for increasing axis stabilization and control by enhancing redundancy.
2. Description of the Prior Art
Angular velocities about the major axes of an aircraft (e.g. fixed wing, rotating wing and flying bodies) provide the primary parameters for the stabilization and control of flight attitude. Such measurements can be taken, for example, by three gyroscopes oriented in the directions of the main axes or by a strapdown device having either three single-axis gyroscopes, (e.g. laser gyroscopes) or two gyroscopes, each with two measurement degrees of freedom (e.g. a dry tuned gyroscope).
The technically feasible reliability of such devices is generally insufficient. As a consequence, multiple redundancy is utilized to increase reliability (i.e. reduce the probability of failure). This requires one to determine the possibly erroneous behavior of one or such redundantly-arranged measuring devices. That determination requires at least three measured values so that a decision (majority voting) can be formed in a computation and decision process.
Simple multiple redundancy arrangements unfortunately increase both weight and cost. In recognition of this, a system in which either of two strapdown devices is arranged at an angle of .alpha..noteq.n1/2.pi. (n=1, 2, . . .) has been proposed. (Sebring, Young 1984, "Application of Multifunction Strap-down Inertial Systems", AGARD Lecture Series No. 133, Advances in Strapdown Inertial Systems). It has been further proposed to equip the sensor block of a strapdown system with several non-orthogonal gyroscopes as the minimum necessary for measurement about three axes in space (Keller 1979, "Ueber redundante Strapdownsensorkonfigurationen der inertialen Ortung und Navigation" (Redundant Strapdown Sensor Configurations in Inertial Position Finding and Navigation), Diplomarbeit, TU Berlin 1979.)
The format approach permits installation of the two devices at different locations in the aircraft and therefore offers decreased vulnerability as well as greater availability of measured values. A disadvantage lies in the fact that the generally-rectangular devices require substantially greater space since they cannot be installed parallel, anti-parallel or orthogonal to the main axes of the aircraft. Special design measures are therefore required, such as special installation fixtures and calibration methods, as opposed to devices which can be installed parallel or anti-parallel to the main axes.
The latter design is limited insofar as the redundancy is generally limited to the gyroscope and associated recording and drive electronics, while redundancy of electronics of the associated digital computer, interfaces and power supply are not considered. Thus, actual failure rates are not considered.